Updated code example for asyncio.gather (GH-20604) (GH-26120)

The previous example did not fully showcase the interest of using gather.

Here the example showcases "the result is an aggregate list of returned values".
(cherry picked from commit 56b8ea6)

Co-authored-by: josephernest <[email protected]>

Co-authored-by: josephernest <[email protected]>

Author: miss-islington

Doc/library/asyncio-task.rst

@@ -360,32 +360,35 @@ Running Tasks Concurrently
       async def factorial(name, number):
           f = 1
           for i in range(2, number + 1):
-              print(f"Task {name}: Compute factorial({i})...")
+              print(f"Task {name}: Compute factorial({number}), currently i={i}...")
               await asyncio.sleep(1)
               f *= i
           print(f"Task {name}: factorial({number}) = {f}")
+          return f
 
       async def main():
           # Schedule three calls *concurrently*:
-          await asyncio.gather(
+          L = await asyncio.gather(
               factorial("A", 2),
               factorial("B", 3),
               factorial("C", 4),
           )
+          print(L)
 
       asyncio.run(main())
 
       # Expected output:
       #
-      #     Task A: Compute factorial(2)...
-      #     Task B: Compute factorial(2)...
-      #     Task C: Compute factorial(2)...
+      #     Task A: Compute factorial(2), currently i=2...
+      #     Task B: Compute factorial(3), currently i=2...
+      #     Task C: Compute factorial(4), currently i=2...
       #     Task A: factorial(2) = 2
-      #     Task B: Compute factorial(3)...
-      #     Task C: Compute factorial(3)...
+      #     Task B: Compute factorial(3), currently i=3...
+      #     Task C: Compute factorial(4), currently i=3...
       #     Task B: factorial(3) = 6
-      #     Task C: Compute factorial(4)...
+      #     Task C: Compute factorial(4), currently i=4...
       #     Task C: factorial(4) = 24
+      #     [2, 6, 24]
 
    .. note::
       If *return_exceptions* is False, cancelling gather() after it